1. Field of the Invention
The present invention relates to a process for manufacturing a vehicle body for automobiles.
2. Description of the Prior Art
In general, the manufacture of a vehicle body for automobiles is carried out through four steps: a pressing step, a welding step, a painting step, and an assembling step, and it is a conventional practice to assemble together individual parts resulting from pressing of steel plates at the pressing step by welding or by use of an adhesive (in many cases, of a dry setting type) at the welding step to complete the build-up of a vehicle body (it is commonly referred to as a white body because it is uncoated). Then, the white body is subjected to a pretreatment, a priming (in general, an electrodeposition coating), a sealing, an intercoating and a topcoating at the painting step, and the vehicle body after completion of the painting is subjected to fitting-out operations for mounting of parts such as an engine, tires, a steering wheel and seats to provide a completed vehicle.
Recently, there has been proposed a process which involves removing doors from the vehicle body which has been coated to conduct the independent fitting-out for the vehicle body and the doors and thereafter effecting the reassembling in order to facilitate the assembling of parts to the interior of the vehicle body for the purpose of full automation of assembling by a robot (see Japanese Patent Application Laid-open No. 8884/78).
However, the above prior art is accompanied by the following various problems:
First, for an adhesive employed at the welding step, a thermal setting type adhesive is commonly used in view of adhesion, durability and term in which such adhesive can be used, to a pressing oil and a corrosion protecting oil deposited on the steel plates. A thermal setting reaction of such adhesive is effected by utilizing a drying oven at the painting step, but repeated heating and cooling as well as attachment of the part with another part occur at the painting step. In addition, the assembling itself is conducted prior to the setting reaction and hence, at the completion of the painting step, a difference in level and a gap between the parts are greater, and hence, a readjustment of assembling is required.
Secondly, treatments recently conducted at the painting step for the purpose of an elimination or reduction of labor and an increase in quality are a full-dipping pre-treatment and an electrodeposition coating, as well as sealing, intercoating and topcoating treatments by means of a robot. To sufficiently deal with a Gap and mating surfaces between the parts in effecting the full-dipping pretreatment and the electrodeposition, it is necessary to maintain the plate-like parts such as a bonnet, a trunk lid and doors in their opened conditions, attendant with a need for a personnel for mounting and removing a holding jig required thereby.
In conducting the sealing, intercoating and topcoating by means of the robot, the coating is not only on the surface of/he vehicle body, but also covers extensive areas such as the back side of the bonnet, the interior of the engine, the back sides of the doors, the interior of a compartment, and the back side of a trunk, and further mating surfaces and a gap between parts and hence, the sealing and coating operations with the opening and closing of the plate-like parts are difficult to a moving function of the robot. Moreover, the coating on the back sides of the parts requires an impossible position for the robot and consequently, there is possibly created a portion which is concealed behind the part itself and is not subjected to a satisfactory coating, resulting in a requirement for a correcting operation.
Yet further, if the robot is allowed to provide the opening and closing of the plate-like parts, the substantial coating time is limited and therefore, an exclusive opening and closing device (Japanese Patent Application Laid-open No. 143876/85) is required. However, if the exclusive opening and closing device is placed into a relatively narrow painting booth, there is a fear of external damages to the vehicle after it has been coated.
In addition, a metallic coating is very often used recently. Such a coating film is formed by application of a base coating containing an aluminum powder and a transparent clear coating in a so-called wet-on-wet manner, and a white body, with the doors and the like as vertical surfaces, is coated while being subjected to an influence of gravity. For this reason, for the-base coating, there is produced a difference in line up of the aluminum powder between the vertical and horizontal surfaces, leading to a delicate difference in appearance of the color. In consideration of a flowing property during drying, a coating design is provided allowing for a limit of sagging of the clear coating on the vertical surface and hence it is difficult to achieve smoothness.
At the assembling step fitting-out steps are performed wherein, parts such as an engine, tires, a steering wheel, seats and panes of glass are assembled to the vehicle body which has been coated, but the plate-like parts must be opened and closed for the assembling, which is inferior in working properties. In addition, the coated surfaces may be damaged during assembling, bringing about an increase in repairing manhours.
Further, with a process in which the doors are removed after coating and independently subjected to fitting-out, as disclosed in Japanese Patent Application Laid-open No. 8884/83, the mating surfaces of the door and the vehicle body are not sufficiently coated and hence, it is necessary to make a repair coating at remounting.
The present invention has been accomplished to overcome the problems associated with the prior art, and it is an object of the present invention to provide a process for manufacturing a vehicle body for automobiles, wherein the automation is facilitated and an improvement in quality is provided.